The effect of environmental contaminants on cancer should be a scientific issue, not a political one. But it is probably too late for that. Industry exploits the uncertainties (for a good account of the phenomenon see Naomi Oreskes and Erik Conway’s book Merchants of Doubt), but so do personal injury and mass-tort lawyers looking for the deepest pockets when they represent plaintiffs with cancer.

Environmental organizations have their own agendas, and that was the problem with the Mother Jones article I described in my previous post. It was not an objective journalistic inquiry but a product of the Center for Public Integrity, which aims to show that hexavalent chromium (aka chromium 6) really did cause a cancer outbreak in the town of Hinkley, California, the site of the Erin Brockovich story. I already described why there is serious doubt that chromium 6 in drinking water is a human carcinogen. Epidemiological studies seem to bear that out. After analyzing the statistics, the State of California found no evidence of a cancer cluster in Hinkley. But the Center for Public Integrity aims to show that the conclusion is not just wrong but part of a cover-up.

“Erin Brockovich’s Biggest Debunker, Debunked,” the headline declares. Then comes a pullout quote, “This guy has got a bias,” and a sidebar and map, “Diluting a Cancer Study.” It implies that an epidemiologist, John Morgan, a professor at the School of Public Health at the University of Loma Linda, gerrymandered the Hinkley statistics at the behest of the chemical industry. The only motivation the reporter could suggest is that Morgan is one of some 350 members of the scientific advisory board of the American Council on Science and Health. (Members also include representatives from the Cincinnati Children’s Health Medical Center, the New York Eye and Ear Infirmary, the Memorial Sloan-Kettering Cancer Center, and the Pathological Institute at the Royal London Hospital.) The Council is largely supported by corporate funding and its agenda is in conflict with that of the Center for Public Integrity.

I think it is a mistake for a scientist or a journalist to identify himself with an advocacy group, and it would be quite a story if Morgan’s affiliation caused him to manipulate the numbers. But I don’t see any reason to believe that he did. In accordance with standard epidemiological procedure, he counted the cancer cases occurring over the years in Hinkley’s official census tract and found that the rate was not significantly higher than that of the general population. Ten years later his followup study came to the same conclusion. Particularly notable was the relatively small number of digestive system cancers — the very kind you would expect if the water had been carcinogenic.

No study like this provides the final word and Morgan describes the weaknesses: residents exposed to chromium 6 may have moved out of the area, and the study did not distinguish between people living closest to the plume and those in outlying areas of the tract. That is typical for a preliminary report. If hints are found of an excess, a far more detailed and expensive investigation is sometimes launched. But the results often turn out to be just as indefinite. The more finely you slice the population, the harder it becomes to produce meaningful statistics. In the dilute doses received by the public, chemical carcinogens apparently cause so few cancers that they barely show up on the epidemiological radar.

The Mother Jones story sees other weaknesses in Morgan’s analysis, all of which are worth considering. Whether they would have affected the outcome is unknown. The Center for Public Integrity’s writer can only conclude what was already obvious: that science cannot say one way or the other whether some residents’ cancers were tied to chromium 6. Statistical studies “aren’t capable of detecting whether a few extra people in a community got cancer from exposure to a toxic chemical.” After the histrionic buildup to the story, it ends with an anti-climax.

The human brain roars against such uncertainty. So we gang up on one side or the other. The truth is left to hover somewhere in between.

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Fire in the Mind

Whether a subtle new pattern shows up in an experiment on the Higgs boson, an epidemiological report about a suspected cancer cluster, or a double-blind trial purporting to demonstrate ESP, it can be maddeningly difficult to distinguish between what we see and what we think we see. "Fire in the Mind" takes a look at the big questions behind today’s science news.

About George Johnson

George Johnson writes about science for the New York Times, National Geographic Magazine, Slate, and other publications. His nine books include The Cancer Chronicles: Unlocking Medicine's Deepest Mystery (August 2013), The Ten Most Beautiful Experiments, A Shortcut Through Time, and Fire in the Mind. He is a winner of the AAAS Science Journalism Award and has twice been a finalist for the Royal Society science book prize. Co-founder and director of the Santa Fe Science Writing Workshop, he can be found on the Web at talaya.net. Twitter @byGeorgeJohnson.